Printed circuit board assemblies (PCBAs) and printed circuit boards (PCBs) are generally tested after being manufactured in order to detect any manufacturing defaults. Generally speaking, PCB testing may be categorized as bare-board testing whereas PCBA testing may be categorized as loaded-board testing. During bare-board testing, a bare PCB, without any components and/or devices attached thereto, is tested to verify the continuity of the traces between the pads and/or the vias on the board. During loaded-board testing, a PCBA with some or all of the electrical components and/or devices mounted thereto is tested in order to verify that all the required electrical connections have been properly completed. Additionally, loaded-board testing may also include integrated circuits (hereinafter “IC” or “ICs”) testing to verify that the components mounted on the PCB perform within specifications.
Previously, PCBAs were generally designed and manufactured such that their electrical contacts, used as test points, were arranged in a regularly spaced pattern or matrix. During testing, the PCBA was placed directly atop of a regularly spaced pattern of interface or testing probes located in a tester. However, as the geometry of PCBAs and electronic components shrunk, PCBAs contact pads could no longer be placed in a regularly spaced pattern and therefore, could no longer be probed directly by regularly spaced interface probes. Consequently, a bare-board fixture was developed which utilized long, leaning solid probes to provide electrical connections between the small, closely spaced, randomly located targets on the PCB and the regularly spaced interface probes located in the tester (see for example U.S. Pat. No. 6,469,531).
A bare-board tester probes testpads, vias, and plated through-holes on bare printed circuit boards only and tests for electrical connectivity and continuity between various test points in the circuits on the printed circuit boards before any components are mounted on the board. A typical bare-board tester contains test electronics with a large number of switches that connect test probes to corresponding test circuits in the electronic test analyzer.
Typical measurements conducted by bare-board testers include shorts, opens and impedance or resistance. Most conventional bare-board testers fall into one of two categories, either the “bed of nails” tester (hereinafter “BON tester”) or the “flying probe” tester.
On the one hand, the BON tester utilizes a dedicated fixture containing a series of plastic sheets with holes drilled therein to permit the passage of the nails. During testing, the UUT is placed in direct contact with the dedicated fixture. The nails on the fixture connect the various targets (e.g., testpads, vias, traces and through-holes) on the UUT to the internal electronics of the tester. Although the BON tester permits nearly simultaneous testing of all targets on a UUT, each unique UUT that is tested requires a different dedicated fixture.
On the other hand, the “flying probe” tester is a universal tester that does not require a fixture. The “flying probe” tester uses a small number of probes that are sequentially positioned over numerous test points on the UUT. Although the “flying probe” tester permits testing of high resolution UUTs, the serial approach of testing targets on a UUT dramatically reduces the throughput of the tester. Thus, the “flying probe” tester is significantly slower than the BON tester. There is therefore a need for an in-circuit testing equipment which will generally obviates the shortcomings of the prior art systems.